Conventionally, for example, in mobile objects such as vehicles and airplanes, so-called head-up displays, which present various information such as texts and speedometers showing progression speed to drivers through windshields, are put to practical use. A representative example of such head-up displays is such that a light beam is emitted from a projecting apparatus such as a projector to a combiner composed of a half mirror or HOE (Holographic Optical Element), and various information is presented to a user by using reflected light from the combiner.
However, in such a head-up display, since the emitted light from the projector and external light are combined by the combiner, when the luminance of the external light is heightened, there is the possibility of difficulty in viewing information projected onto the combiner. For example, when the head-up display is tried to be used in the daytime where the irradiation amount of natural light is large, there is the possibility of difficulty in viewing projected information due to an influence of the natural light. Further, even during evening hours, for example, there is the possibility of difficulty in viewing projected information due to an influence of a headlight of an oncoming car or the like. Therefore, conventionally, for example, it is proposed that a light control apparatus for adjusting the transmission amount of external light is provided onto the combiner, the light amount of the external light transmitting through the combiner is adjusted, and thus deterioration in visibility of information due to the external light is prevented (see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 5-104980